Late-onset Methemoglobinemia Induced by Metobromuron/metolachlor

Received 18 September 2008; received in revised form 16 October 2008; accepted 11 December 2008.

Abstract

The herbicide, Galex, containing 25% of metolachlor and 25% of metobromuron dissolved in 46.7% emulsifiable concentrate was widely used for the control of grasses and broad-leaf weeds in the 1990s and continues to be used today. Metobromuron, a substitute urea herbicide, may cause methemoglobinemia in humans, but very few studies are available about the harmful effects on humans. We report here a case where a 47-year-old man developed severe methemoglobinemia 10 hours after ingestion of 1000 mL of Galex. Acute hypoxic respiratory failure with coma occurred suddenly. After ventilator support was instituted, intravenous methylene blue (1%, 2 mg/kg) was administrated immediately. A second dose of methylene blue was given because of a persistent high level of methemoglobin 2 hours later. The patient was weaned from the ventilator on day 4. However, hemolytic anemia, possibly due to the administration of methylene blue, occurred and persisted to day 11. This resolved gradually only after multiple blood transfusions. Ingestion of a large volume of herbicide containing metobromuron, a substituted urea herbicide, can induce late-onset methemoglobinemia in humans and, while rare, may be fatal if not observed for a sufficient time in the emergency department. Death is possible following the ingestion of this herbicide when adequate diagnoses and treatment are not instituted. Methylene blue is useful in reversing methemoglobinemia, but the side effects such as hemolytic anemia should be monitored, especially at doses exceeding 4 mg/kg or in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency. Clinicians should consider the relevant history of G6PD deficiency before using methylene blue to decrease the risk of unnecessary hemolytic anemia. Methemoglobinemia in patients with G6PD deficiency is best treated with blood transfusions.

Keywords: Methemoglobinemia , Metobromuron , Metolachlor , Methylene blue

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Article Outline

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References

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a Division of Nephrology, Buddhist Tzu Chi General Hospital, Hualien, Taiwan

b School of Medicine, Tzu Chi University, Hualien, Taiwan

c Division of Medical Intensive Care Unit, Department of Internal Medicine, Buddhist Tzu Chi General Hospital, Hualien, Taiwan

d Institute of Medical Sciences, Tzu Chi University, Hualien, Taiwan

Corresponding author. Division of Medical Intensive Care Unit, Department of Internal Medicine, Buddhist Tzu Chi General Hospital, 707, Section 3, Chung-Yang Road, Hualien, Taiwan

PII: S1016-3190(09)60066-5

doi:10.1016/S1016-3190(09)60066-5

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